Solvent extraction process



Patented Jan. 8, 1952 TED STATES ENT F F I CE :ISQLVENT;;EXTRACTION PROCESS Clark J. Egan, Piedmont, Calif., assignor to California "Research Corporation, San Francisco, Calif.,-'a corporationoi Delaware No Drawing. Application June 25, 1948,

Serial No. 35,279

fi' Cla'ims. *1 The present invention" relates to a method .of treating hydrocarbon mixtures containing saturated-and unsaturated hydrocarbons to separate 'a" relatively saturated extract and alrelatively unsaturatedraflinate, and more particularly, .to a

method of selectively dissolving and removing a minor relatively saturated'hydrocarbon fraction from a'petroleumdistillate comprising a minor proportion .of relatively saturated hydrocarbons and -a .maj or proportion of relatively unsaturated hydrocarbons.

The solvent extractionprocesses now in-com- 4 mer'cial use'provide ameans for separatlngminor "proportions ofunsaturatedhydrocarbons such as aromatics and olefins from hydrocarbon mixtures consisting predominantly of more saturated ,hydrocarbons such as paraffins and nap'lithenes.

" These'processes are not Well adapted to the separation-of hydrocarbon mixtures containing-only minor proportions of relatively "saturated hydrocarbons, that is, hydrocarbons in which the hydrogen has been completely replaced by fluorine, are selective for the relatively saturated"hydrocarbons as IODDOSGdltO the relatively unsaturated hydrocarbons. For instance, if a mixture of aromatic and paraifinic hydrocarbons is contacted with a perfiuorocarbon, the parafiinic, hydrocarbons are selectivelydissolved in therperfluorocarbon, 'a'lovver extract phase which comprises per'fluorocarbon and dissolved *parafiinic "hydrocarbons is formed, and an upperraifinatephase 'comprising aromatic hydrocarbons is formed. The phases may beseparatedand a para'fiin rich extract and an aromatic-rich raffinate may be recovered. I

The critical solution "temperaturesiof several typical perfiuorocarbons withanumber offhydrocarbons have-been determined. 1 These temperatures are determined asian aniline pointiisdetermined; the perfluorocarbon and the hydrocarbon beingmixed, usually in approximately equal voluimes, at a temperature"sufficientlylow that two phases exist. The 'temperatureis then-gradually raised until the critical solution temperature, in-

dicated by the formation of a single homogeneous phase, is reached. The 'followingTable 1 shows the critical'solutiontemperatures of several perfluoro-carbons with a number of hydrocarbons, temperatures being recorded in degrees Fahren ,heit.

TABLEI Critical Solution Temperatures Solvent "Hydrocarbon TPerfluorm' Perfluoro- ""M'eth'yl Dimethyl fg f g g A flyclohexane Cyclohexane u Methyl Cyclohexan .7

Heptene-l :n-HeXane I 2 27i Trimethyl Pentane n-Pentane (lyclohexane Difierences'in critical solution temperature are 'a measure of the :selectivity of the perfluorocarbon solvents for the several hydrocarbons and hydrocarbon types shown in Table l, the perfiuorocarbon being more selective for those hydrocarbons with which it shows .the lowest critical solution temperatures. It may be seen from the table that the-fiuorocarbons are more selective for "paraffins, olefins andnaphthenes than for aromatics. Itinay alsobe seen that within a narrow molecular weight -range, for instance, the range of thecvhydrocarbons, the critical solution temperature is lowest for normal heptane and successively higher miscibility temperatures are shown for heptane-1, methyl cyclohexane, and

Thefollowing Table 2 shows representative average selectivities, as measured by difference of critical solution temperatures, of several perfiuorocarbons for several mixtures of two hydrocarbon types. The temperature difierences are recorded in degrees Fahrenheit and the values given are for mixtures in which the representatives of the hydrocarbon types boil within a narrow range, the difierence in their boiling points being usually less than F. The hydrocarbon for which the perfiuorocarbons are selective, i. e., have the lowest critical solution temperatures, is written first in the left-hand column of Table 2.

TABLE 2 Selectivities of. perfluorocarbons for a particular hydrocarbon in a binary mixture not shown may.

be obtained by adding the tabulated values. .For example, the selectivity of perfluoromethyl cyclohexane for a branched-chain paraflin from a mixture of that compound with an aromatic will readily removed from such cuts by the perfluorobe indicated by the sum of 40, and 85, that is,

by a critical solutiontemperature difference of 160 F.

From the tables it is seen that the perfluorocarbons may be advantageously employed as extractive solvents to'remove minor amounts of paraffinic, olefinic and/or naphthenic hydrocarbons from a stock consisting predominantly of aromatic hydrocarbons. For example, the extract obtained by sulfur dioxide extraction of naphtha or kerosene contains minor amounts of non-aro-.

matic hydrocarbons which may be removed from such extracts by a further extraction of the sul fur dioxide extract with a perfluorocarbon. Various highly aromatic cuts are separated from petroleum distillates for use as thinners or solvents or as base stocks in chemical synthesis. aromatic cuts may be purified and their value for the intended use enhanced by extraction with a perfiuorocarbon to remove non-aromatic constituents and separate a highly aromatic raffmate. is separated from catalytically reformed naphtha to serve as a source of ortho xylene for oxidation to phthalic anhydride. The presence of minor quantities of non-aromatic hydrocarbons in this cut is undesirable and they may be extracted with perfluorocarbons. As a further example, a highly aromatic toluene cut may be separated from catalytically reformed naphtha. The minor proportion of non-aromatic hydrocarbons contained in the toluene cut may be extracted with a perfluorocarbon and a nitration grade toluene ramnate can be recovered.

Perfiuorocarbons may be employed to separate diverse hydrocarbon mixtures such as petroleum fractions, shale oil fractions, or Fischer-Tropsch synthesis fractions, which have broad boiling osene, into a relatively saturated extract and a These 7 For example, a highly aromatic xylene cut 4 relatively unsaturated raifinate. In such cases a 7 more complete separation may be obtained by carbon. A first extract fraction may be separated which comprises branched-chain paraffins. From the raifinate of the first extraction a second extraction may be made to separate a second extract fraction comprising normal paramns and olefins, no attempt being made to separate these latter types. From the railinate of the second extraction step a third extraction may be made to separate an extract comprising naphthenes and a final raifinate comprising aromatic hydrocarbons. The perfluorocarbons may be employed to efiect the separation of acyclic and cyclic hydrocarbons by adjusting the solvent to oil ratio according to the character of the stock. In this case the solvent is employed in sufiicient amount to extract the isoparaffins, normal paramns and olefins leaving naphthenes and aromatics as the raffinate.

The perfluorocarbons may also be employed to separate hydrocarbon mixtures of less diverse composition than petroleum distillates. Hydrocarbon mixtures consisting essentiallyof only two hydrocarbon types may be separated. For example, the reaction product of a paraffin isomerization reaction may be extracted with a perfluorocarbon to remove the branched-chain isomers as an extract leaving relatively straight-chain hydrocarbons in the raninate which may be recycled to the isomerization step.

The following examples illustrate the employment of the perfluorocarbons to separate hydrocarbon mixtures in the manner above described.

EXAMPLE 1.

A mixture of 53.7 volume per cent normal heptane and 46.3 volume per cent benzene was extracted with perfluoromethyl cyclohexane. An upper rafiinate phase comprising hydrocarbons and a lower extract phase comprising perfluoromethyl cyclohexane and hydrocarbons were separated. The composition of the hydrocarbons contained in both phases was determined by analysis. The extraction coefiicient, beta, was calculated according to the formula:

Heptane in Extract Benzene in Extract Heptane in Rafiinate Benzene in Raffinate The amounts of benzene and heptane in the extract and raflinate were expressed in volume per cent on a perfluorocarbon-free basis. The value of the extraction coeilicient was found to be 2.5.

EXAMPLE 2 A mixture of 21.7 volume per cent heptane and 78.3 volume per cent benzene was extracted with perfluoro-methyl cyclohexane. Phase separation, analysis, and calculation of the extraction coefiicient were made as in Example 1. The extraction coefficient was found to be 2.3.

The examples illustrate the selectivity of the perfluorocarbons for the paraffinic component of a parafiin-aromatic mixture. This selectivity is opposite to that shown by such solvents as sulfur dioxide and furfural which selectively dissolve the aromatics from such mixtures.

The high liquid densities, 1.5-2.0 g./cc. of the perfluorocarbons facilitate phase separation in Beta:

scribed.

It has been found that hydrocarbons boiling above the boiling range of kerosene, that is, above about 550 F., may not readily be separated by extraction with perfiuorocarbons due to the low solubilities of such hydrocarbons in perfluorocarbon solvents. Accordingly, it is preferred to treat petroleum distillates boiling in the boiling range of gasoline and kerosene with perfluorocarbon solvents to efiect their separation according to the invention.

It is also preferred to employ per-fluorocarbon solvents containing at least three and not more than twelve carbon atoms. Lighter perfiuorocarbons have very low boiling points and require considerable pressures to maintain the desired liquid phase conditions in the extraction process. Perfluorocarbons containing more than twelve carbon atoms have reduced solubilities for the hydrocarbons so that the solvent-hydrocarbon ratio required in making separations becomes very high.

It may be seen from the examples that the extraction coefiicients are not large, accordingly several stages of extraction may be needed and may be provided where a high degree of separation of the components of a hydrocarbon mixture is desired.

I claim:

1. The method of separating a petroleum distillate boiling in the boiling range of gasoline and kerosene and containing parafiini 'oleiinic, naphthenic and aromatic hydrocarbons which comprises first extracting the distillate with a perfluorocarbon containing 3 to 12 carbon atoms to separate an extract comprising parafiins and olefins, and extracting the rafiinate of the first extraction with a perfiuorocarbon containing 3 to 12 carbon atoms to separate an extract comprising naphthenic hydrocarbons.

2. A method of separating components of a mixture of normally liquid cyclic and acyclic hydrocarbons boiling below 550 F. in which the cyclic hydrocarbons predominate which comprises contacting said mixture in the liquid phase with a perfiuorocarbon containing 3-12 carbon atoms under conditions forming a two-phase system and selectively separating a solvent extract containing predominantly acyclic hydrocarbons.

3. A method of separating components of petroleum fractions boiling in the range of gasoline and kerosene which comprises contacting said fractions in the liquid phase with a perfluoro-- carbon containing 3-12 carbon atoms to produce a separation into two phases and selectively separating the perfiuorocarbon extract phase containing predominantly acyclic hydrocarbons.

4. A method of separating components of a mixture of normally liquid aromatic and nonaromatic hydrocarbons boiling below 550 F. in which the aromatic hydrocarbons predominate which comprises contacting said mixture in the liquid phase with a perfiuorocarbon containing 3-12 carbon atoms to produce a separation into two phases and selectively separating a perfluorocarbon extract phase containing predominantly non-aromatic hydrocarbons.

5. A method of separating components of a normally liquid hydrocarbon mixture boiling below 550 F. containing a minor proportion of paraffinic hydrocarbons which comprises contacting said mixture in the liquid phase with a perfiuorocarbon containing 3-12 carbon atoms to produce a separation into two phases and selectively separating a perfiuorocarbon extract phase containing a major proportion of parafiinic hydrocarbons.

6. A method of separating components of a mixture of normally liqui'd hydrocarbons boiling below 550 F. containing a minor proportion of branched chain parafiinic hydrocarbons which comprises contacting said mixture in the liquid phase with a perfluorocarbon containing 3-12 carbon atoms to separate a solvent extract containing a major proportion of branched chain parafiins.

CLARK J. EGAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,136,767 Ferres et al Nov. 15, 1938 2,162,682 Ferres et a1 June 13, 1939 2,249,461 Diwoky July 15, 1941 2,343,611 Cope et a1 Mar. 7, 1944 

1. THE METHOD OF SEPARATING A PETROLEUM DISTILLATE BOILING IN THE BOILING RANGE OF GASOLINE AND KEROSENE AND CONTAINING PARAFFINIC, OLEFINIC, NAPHTHENIC AND AROMATIC HYDROCARBONS WHICH COMPRISES FIRST EXTRACTING THE DISTILLATE WITH A PERFLUOROCARBON CONTAINING 3 TO 12 CARBON ATOMS TO SEPARATE AN EXTRACT COMPRISING PARAFFINS AND OLEFINS, AND EXTRACTING THE RAFFINATE OF THE FIRST EXTRACTION WITH A PERFLUOROCARBON CONTAINING 3 TO 12 CARBON ATOMS TO SEPARATE AN EXTRACT COMPRISING NAPHTHENIC HYDROCARBONS. 